It is well-known that liquid crystal display (LCD) is not a self-emission display device. A backlight module is a key component of the LCD for providing light source having sufficient brightness and uniform distribution, so that the LCD can display image properly. Currently, the backlight module mainly comprises a light source, a light guiding plate (LGP) and optical sheets. In general, a lamp or a light emitting diode (LED) is used as the light source. The light guiding plate is mainly designed to change path of the lights so as to guide lights emitted from the light source toward a desired direction. The optical sheet is mainly designed to converge lights, so that the backlight module emits uniform lights.